Issued  i  -i 


0  J|:=  U.  S.  DEPARTMENT  OF  AGRICULTURE, 

1    I  BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  No.  93. 

0     —  -  A.  D.  MELV1N,  CHIEF  OF  BUREAU. 

8  1 

3  = 


iHE  RELATION  OF  TUBERCULOUS  LESIONS 
TO  THE  MODE  OF  INFECTION. 


E.  C.  SCHROEDER,  M.  D.  V., 

Superintendent  of  l^.\pfrinient  Station, 
^  Bureau  of  Animal  lndustr\ , 

5 

r0    2.  AND 

W.  E.  COTTON, 

p     5[     ££  Expert  Assistant  at  Experiment  Station, 

J~jj     »-i   ^<J  Bureau  of  Animal  Industry. 


P 
O 


P 


WASHINGTON: 
GOVERNMENT    PRINTING    OFFICE. 

1906. 


Issued  Di-cciiilit-rSl,  1906. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  No.  93. 

A.  D.  MELVIN,  CHIEF  OP  BUREAU. 


THE  RELATION  OF  TUBERCULOUS  LESIONS 
TO  THE  MODE  OF  INFECTION. 


BY 


E.  C.  SCHROEDER,  M.  D.  V., 

Superintendent  of  Experiment  Station, 
Bureau  of  Animal  Industry, 

AND 

W.  E.  COTTON, 

Expert  Assistant  at  Experiment  Station, 
Bureau  of  Annual  Industry. 


WASHINGTON: 
GOVERNMENT    PRINTING   OFFICE. 

1906. 


BUREAU  OF  ANIMAL  INDUSTRY. 


Chief:  A.  D.  MELVIN. 

Assistant  Chief:  A.  M.  FARRINGTON. 
Chief  Clerk:  E.  B.  JONES. 
Biochemic  Division:  MARION  DORSET,  chief. 

Dairy  Division:  ED.  H.  WEBSTER,  chief;  C.  B.  LANE,  assistant  chief. 
Inspection  Division:  RICE  P.  STEDDOM,  chief;  U.  G.  HOUCK,  associate  chief;  MORRIS 
WOODEN,  assistant  chief. 

.  Pathological  Division:  JOHN  K.  MOHLER,  chief. 
Quarantine  Division:  RICHARD  W.  HICKMAN,  chief. 
Division  of  Zoology:  BRAYTON  H.  RANSOM,  chief. 
Animal  Husbandman:  GEORGE  M.  ROMMEL. 
Editor:  JAMES  M.  PICKENS. 


EXPERIMENT    STATION. 


Superintendent:  E.  C.  SCHROEDER. 
Expert  Assistant:  W.  E.  COTTON. 
2 


LETTER  OF  TRANSMITTAL. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY, 
Washington,  D.  C.,  Novembers,  1906. 

SIR:  I  have  the  honor  to  transmit  herewith,  for  publication  as  a  bul- 
letin of  this  Bureau,  an  article  entitled  "The  Relation  of  Tuberculous 
Lesions  to  the  Mode  of  Infection,"  by  Dr.  E.  C.  Schroeder  and  W.  E. 
Cotton,  of  the  Experiment  Station  of  this  Bureau. 

In  the  experiments  described  in  this  paper,  which  were  carried  out 
mainly  for  the  purpose  of  further  testing  the  susceptibility  of  the  lung 
to  infection  with  tubercle  bacilli  regardless  of  the  point  at  which  the 
infectious  material  enters  the  body,  tuberculosis  was  produced  in  the 
lungs  of  a  calf  and  three  hogs  by  inoculation  near  the  end  of  the  tail. 
This  work,  taken  in  connection  with  that  reported  in  Bulletins  Nos.  86 
and  88  of  this  Bureau,  indicates  that  the  lungs  may  readily  become  the 
seat  of  tuberculous  disease  no  matter  thru  what  channel  the  bacilli 
gain  entrance  into  the  body,  and  that  the  location  of  lesions  in  the 
lungs  can  no  longer  be  considered  as  reliable  evidence  that  the  infec- 
tion entered  thru  the  respiration. 

Dried  sputum  has  long  been  regarded  as  the  rnost  prolific  agent  in 
the  dissemination  of  tuberculosis  among  people,  but  the  facts  pre- 
sented in  this  bulletin,  which  are  believed  to  have  an  important  bearing 
on  the  problem  of  how  tuberculosis  is  contracted  by  human  beings,  go 
to  show  that  too  much  importance  has  been  attached  to  this  and  not 
enough  to  the  more  serious  danger  from  fresh  or  moist  tuberculous 
material  which  enters  human  food  in  many  ways,  one  of  the  commonest 
of  which  is  attributable  to  the  tuberculous  dairy  cow. 
Respectfully, 

A.  M.  FARRINGTON, 

Acting  Chief  of  Bureau. 
Hon.  JAMES  WILSON, 

Secretary  of  Agriculture. 

3 


CONTENTS. 


Page. 

Introductory 7 

The  experiments  with  cattle 7 

The  experiments  with  hogs 9 

The  course  of  the  infection  from  tail  to  lung 10 

Some  corroborative  evidence  of  other  investigators 12 

The  inhalation  and  ingestion  methods  of  infection  contrasted 12 

The  theory  of  infection  by  inhaling  dried  sputum 13 

The  more  serious  danger  from  fresh  and  moist  tuberculous  material 13 

The  facility  with  which  bacilli  from  tuberculous  cows  may  enter  human  food.  14 

Conclusions ., 16 

Summary  of  the  conclusions 17 

Addendum .• 18 

Recent  work  by  a  French  investigator 18 

5 


THE  RELATION  OF  TUBERCULOUS  LESIONS  TO  THE 
MODE  OF  INFECTION. 


INTRODUCTORY. 

It  is  an  established  and  generally  admitted  fact  that  tuberculosis  is 
more  commonly  an  affection  of  the  lung  than  of  other  organs  or  struc- 
tures of  the  bod}'.  In  a  recent  publication  of  the  Bureau  of  Animal 
Industry a  experimental  evidence  was  presented  to  support  the  con- 
clusion that  this  relativel}T  greater  frequency  of  pulmonary  tubercu- 
losis, as  compared  with  other  forms,  is  not  due  to  the  more  direct 
exposure  of  the  lung  to  infection  that  reaches  it  from  without,  sus- 
pended in  the  respired  air,  but  to  the  more  direct  exposure  of  the  lung 
to  infection  that  may  have  entered  the  body  in  any  way  and  has 
reached  the  lymph  channels  and,  thru  them,  the  blood  stream. 

To  obtain  further  information  on  this  subject  and  to  trace  more 
precisely  the  course  taken  by  the  infectious  material  from  its  point  of 
entrance  into  the  body  to  the  lung,  five  animals — three  hogs  and  two 
cattle — were  given  subcutaneous  injections  of  virulent  tubercle  bacilli. 
The  seat  of  injection  selected  as  the  most  favorable  for  the  purpose 
was  the  tail,  as  near  the  extreme  end  of  it  as  possible,  as  this  is  the 
farthest  removed  available  portion  of  the  bod}"  from  the  lung,  and 
the  location  from  which  the  infection  of  the  latter  seemed  least  likely 
to  occur. 

THE  EXPERIMENTS  WITH  CATTLE. 

The  records  of  the  two  cattle  above  mentioned,  together  with  an 
additional  experiment  on  a  calf;  are  as  follows: 

Heifer  No.  398. — About  6  months  old,  in  excellent  condition. 
Tested  with  tuberculin  without  reaction.  Injected  April  6,  1906,  sub- 
cutaneously,  immediately  above  the  brush  at  the  end  of  the  tail,  with 
one-half  cubic  centimeter  of  a  virulent  bovine  tubercle  culture.6 

Bull  No.  399. — About  6  months  old,  in  excellent  condition,  tested 
with  tuberculin  without  reaction.  Injected  April  6,  1906,  subcutane- 
ously,  immediately  above  the  brush  at  the  end  of  the  tail,  with  1  cubic 
centimeter  of  virulent  bovine  tubercle  culture. 

a  Bulletin  No.  86. 

&The  culture  used  is  known  in  the  laboratories  of  the  Bureau  of  Animal  Industry 
as  Bovine  III,  and  has  been  kept  under  artificial  cultivation  for  a  number  of  years. 


8  TUBERCULOUS    LESIONS    AND   MODE    OF    INFECTION. 

The  result  from  the  injections  was  a  slight  induration  at  the  ends  of 
the  tails.  The  cattle  were  killed  on  June  13,  1906  (sixty-eight  days 
after  the  injections  were  made),  and  examined  post-mortem.  No  lesions 
of  disease  were  found  excepting  a  few  pearl-like  nodules  in  the  lungs, 
directly  under  the  pleurae,  of  both  animals,  and  two  such  nodules  in 
the  liver  of  one  animal.  Microscopic  examination  showed  the  nodules 
to  be  little  fatty  tumors  and  wholly  nontuberculous  in  character. 

The  absence  of  disease  in  the  two  cattle  suggested  the  idea  that  an 
injection  of  the  kind  they  received  could  be  used  for  purposes  of 
immunization  against  tuberculosis,  and  hence  several  young  cattle 
were  injected  under  the  skin  of  their  tails  in  a  separate  experiment 
relative  to  immunization.  Among  the  animals,  one  (No.  461)  died  on 
the  twenty  -third  day  after  injection.  Its  autopsy  record,  which  is 
given  below,  is  of  special  interest.  The  other  animals  of  the  group 
will  be  treated  in  a  separate  publication  at  a  later  date. 

Calf  No.  Jf.61. — Three  months  old,  tested  with  tuberculin  without 
reaction.  Injected  June  23,  1906,  subcutaneously,  at  the  end  of  its 
tail,  with  bovine  tubercle  culture  (the  tubercle  bacilli  used  were 
Bovine  III,  the  same  kind  as  used  for  cattle  Nos.  398  and  399).  On 
Jul}7  15,  1906,  the  calf  died,  and  on  post-mortem  examination  the  fol- 
lowing lesions  were  found: 

The  tail,  at  the  seat  of  inoculation,  is  slightly  thickened,  and  the  subcutaneous  tis- 
sues are  edematous,  streaked  with  hemorrhagic  lines,  and  contains  irregular  masses 
of  necrosis. 

One  lymph  gland,  anterior  to  and  a  little  to  the  right  of  the  insertion  of  the  tail, 
embedded  in  the  coccygeal  muscles,  is  ]£  by  1  by  $  inch  in  dimensions,  and  is 
edematous,  intensely  congested,  and  has  the  appearance  of  being  affected  thruout 
with  very  recent  tuberculous  disease.  Microscopic  examination  of  the  gland  shows 
innumerable  tubercle  bacilli.  The  corresponding  gland  on  the  left  side  is  not  more 
than  a  tenth  as  large,  but  otherwise  in  the  same  condition. 

The  superficial  inguinal,  prepectoral,  prescapular,  axillary,  bronchial,  mediastinal, 
gastro-hepatic,  and  mesenteric  glands  are  edematous  and  marked  with  hemorrhagic 
lines  and  points.  Microscopic  examination  of  these  glands  shows  innumerable 
tubercle  bacilli  in  the  superficial  inguinal  and  mesenteric  glands,  a  few  in  the  media- 
stinal  glands,  one  doubtful  bacillus  in  two  preparations  from  the  bronchial  glands, 
an< I  not  any  in  the  other  glands. 

The  entire  lung  has  a  firm,  solid  character  and  does  not  collapse  atall.  Tin-  lower 
halves  <if  tin-  cephalic  and  median  lobes,  the  entire  azygos  lobe,  and  large  patches  in 
the  principal  lobes  are  of  a  dark  red,  hemorrhagic  appearance.  The  whole  lung,  on 
surface  ami  >ection,  is  densely  and  evenly  sprinkled  with  minute  yellow  areas  about 
one-thirtieth  of  an  inch  in  diameter,  which  are  made  up  of  aggregations  of  very 
minute  necrotic  points.  All  the  surface  lesions  are  beneath  the  capsule,  and  the 
number  of  lesions  is  so  great  that  more  lung  tissue  is  involved  than  is  left  unaffected. 
.Microscopic  examination  of  the  little  yellow  areas  shows  the  presence  of  innumerable 
tubercle  bacilli.  f  ' 

Tin'  liver,  spleen,  kidneys,  stomachs,  and.  intestine  are  in  apparently  normal 
condition. 

The  case  is  a  perfect  picture  of  fatal  miliary  tuberculosis  of  the  lung 
of  recent  origin,  with  a  rapidly  developing  infection  of  the  lymphatic 


EXPERIMENTS    WITH    HOGS.  9 

glands  generally.  The  affection  of  the  lung  was  so  extensive  that 
death  was  probably  due  directly  to  suffocation.  The  rapid  character 
of  the  disease  and  the  early  fatal  termination  are  attributable  to  the 
extreme  susceptibility  of  this  particular  calf  to  tuberculosis. 

THE  EXPERIMENTS  WITH  HOGS. 

The  records  of  the  three  hogs  are  as  follows: 

Hogs  Nos.  1383,  1384,  and  1385  were  tested  with  tuberculin  without 
reaction  on  April  4,  1906,  and  each  received  on  April  6,  1906,  an 
inoculation  of  tubercle  culture,  Bovine  III,  under  the  skin  covering 
the  dorsal  surface  of  the  tail  just  anterior  to  its  end.  The  hogs  were 
killed  a  little  more  than  two  months  later  and  examined  post-mortem. 
The  autopsy  records  follow : 

Hog  No.  1383. — June  12,  1906,  killed  and  examined  post-mortem.  At  the  time  of 
death  the  animal  seemed  very  much  distrest  and  gave  the  impression  that  it  would 
die  within  a  few  hours.  General  condition  very  good,  fat,  weight  about  200  pounds. 
The  seat  of  the  inoculation  in  the  tail,  about20cm.  (Sinches)  from  its  point  of  attach- 
ment to  the  body,  shows  considerable  connective  tissue  thickening.  The  superficial 
inguinal  glands  contain  several  small  tuberculous  areas. 

The  lung  is  adherent  to  the  chest  wall  and  diaphragm,  and  the  various  lobes  to 
each  other.  Sprinkled  evenly  over  and  thruout  its  entire  substance  are  innumer- 
able tuberculous  masses  from  1  mm.  to  1  cm.  in  diameter;  fully  one-half  of  the  lung 
tissue  is  destroyed.  The  pulmonary  and  costal  pleune  and  the  thoracic  surface  of 
the  diaphragm  are  thickly  studded  with  innumerable  tubercles  from  1  mm.  to  1  cm. 
in  diameter. 

The  convex  surface  of  the  liver  is  sprinkled  with  minute  tubercles;  a  similar  but 
less  marked  condition  is  found  on  the  concave  surface.  No  tubercles  were  found  in 
the  parenchyma  of  the  organ. 

No  lymph-gland  disease  was  found  in  any  part  of  the  body  excepting  that 
recorded  in  the  superficial  inguinal  glands. 

Hog  No.  1384- — June  13,  1906,  killed  and  examined  post-mortem.  General  condi- 
tion very  good,  fat,  weight  about  200  pounds.  The  tail,  about  25cm.  QO  inches) 
from  its  point  of  attachment  to  the  body,  at  the  seat  of  inoculation,  is  somewhat 
thickened.  On  section  the  increased  connective  tissue  is  found  to  be  sprinkled  with 
a  dozen  or  more  minute  necrotic  foci,  less  than  one-half  mm.  in  diameter.  One  of  the 
superficial  inguinal  glands  contains  a  few  tuberculous  foci. 

The  lung  is  adherent  to  the  chest  wall  and  to  the  diaphragm.  The  costal  and  pul- 
monary pleune  and  the  thoracic  surface  of  the  diaphragm  are  closely  sprinkled  with 
small  tubercles  which  vary  in  size  from  points  to  3  mm.  in  diameter.  The  cephalic 
lobes  on  both  sides,  the  entire  left  median  lobe,  the  anterior  and  dependent  portions 
of  the  right  median  lobe,  and  the  anterior  portions  of  both  principal  lobes  are  com- 
pletely solidified  and  tuberculous  thruout;  the  balance  of  the  lung  is  sprinkled  evenly 
with  innumerable  tuberculous  areas  from  1  mm.  to  1  cm.  in  diameter.  The  bronchial 
glands  on  both  sides  are  greatly  enlarged  and  sprinkled  with  a  small  number  of  very 
minute  necrotic  foci. 

The  liver  is  evenly  sprinkled  with  innumerable  foci  of  tuberculosis,  2  mm.  and  less 
in  diameter.  The  gastro-hepatic  chain  of  lymph  glands  are  enlarged  and  sprinkled 
with  minute  foci  of  tuberculosis.  The  spleen  contains  a  sprinkling  of  tuberculous 
foci. 

Hog  No.  1385. — June  13,  1906,  killed  and  examined  post-mortem.  General  condi- 
tion very  good,  fat,  weight  about  200  pounds.  The  tail,  about  20  cm.  (8  inches) 
13619— No.  93—06—2 


10  TUBERCULOUS    LESIONS    AND    MODE    OF    INFECTION. 

from  its  point  of  attachment  to  the  body,  at  the  seat  of  inoculation,  is  somewhat 
thickened,  and  has  on  its  lower  surface  a  flat  sore  about  2  cm.  in  diameter.  On  sec- 
tion the  thickening  is  found  to  be  due  to  an  increase  in  the  amount  of  connective 
tissue. 

One  of  the  right  superficial  inguinal  glands  is  enormously  enlarged,  fully  ten  times 
its  normal  diameter,  and  completely  tuberculous.  The  corresponding  gland  on  the 
left  side  is  slightly  enlarged  and  contains  a  few  tuberculous  foci. 

The  lung  is  adherent  to  the  chest  wall  by  a  number  of  fine  connective  tissue  threads. 
The  entire  organ  is  densely  and  evenly  sprinkled  with  innumerable  tuberculous 
masses  from  1  to  5  mm.  in  diameter.  The  tubercles  are  so  numerous  that  fully  one- 
third  of  the  entire  lung  tissue  has  been  displaced  by  them. 

The  liver  contains  about  a  dozen  minute  tubercles  1  mm.  and  less  in  diameter. 

Spleen  contains  about  a  dozen  tubercles  less  than  1  mm.  in  diameter. 

No  lesions  of  the  lymph  glands  were  found  excepting  those  recorded  for  the  super- 
ficial inguinals. 

THE  COURSE  OF  THE  INFECTION  FROM  TAIL  TO  LUNG. 

The  post-mortem  examinations  of  the  three  hogs  and  the  one  calf 
that  became  affected  with  tuberculosis  show  the  most  extensive  lesions 
in  the  lung  in  every  case.  When  we  bear  in  mind  that  this  resulted 
from  tubercle  bacilli  introduced  into  the  bodies  of  the  animals  by  sub- 
cutaneous inoculations  at  the  ends  of  their  tails,  we  are  justified  in  con- 
cluding that  one  of  two  courses  was  taken  by  the  bacilli  to  reach 
the  lung:  (1)  They  were  taken  up  b}^  the  eapillaiy  blood  vessels  and 
carried  to  the  lung  directly  with  the  venous  blood  stream;  or  (2)  they 
were  taken  up  by  the  lymph  radicals,  past  along  the  lymph  channels 
by  or  thru  the  lymph  glands,  entered  the  great  thoracic  duct,  and  thru 
it  were  poured  into  the  venous  circulation. 

Once  tubercle  bacilli  have  entered  the  venous  blood  stream  there  is 
nothing  in  the  way  of  the  direct  infection  of  the  lung  except,  first, 
smooth-walled  vessels  of  constantly  increasing  caliber,  second,  the 
smooth- walled  chambers  of  the  heart,  and  third,  the  smooth- walled 
pulmonary  arteries  that  end  in  the  exceedingly  fine,  thin-walled,  com- 
plex capillary  system  of  the  lung,  the  anastomosis  of  which  is  so  com- 
plete and  the  close  and  intricate  intercommunication  so  frequent  that 
it  is  not  difficult  to  conceive  of  individual  vessels  in  which  perfect 
stasis  may  occur. 

The  destruction  of  tubercle  bacilli  by  leucocytes  or  phagocytes  after 
they  have  entered  the  blood  dors  not  require  consideration  in  this  con- 
nection, nor  the  attenuation  of  the  bacilli  by  the  germicidal  action  of  the 
blood  for  various  other  species  of  bacteria.  If  these  were  factors  of 
importance  against  tin-  infection  of  an  organ  with  tuberculosis  it  would 
have  been  impossible,  as  has  been  done  in  some  of  our  earlier  work." 
to  demonstrate  the  persistence  of  live  tubercle  bacilli  of  an  original 
virulence  too  low  to  cause  a  progressive  affection  in  the  tissues  of 
cattle  for  period^  of  time  varying  from  three  month-  to  two  years. 

«  Bureau  of  Animal  Industry  Mullctin  NH.  A:.',  1'art  III. 


COURSE  OF  INFECTION  FROM  TAIL  TO  LUNG.         11 

In  this  connection  it  may  be  interesting1  to  give  an  observation  made 
at  the  Experiment  Station  on  two  cows,  each  of  which  received  an 
injection  of  tubercle  bacilli  into  a  quarter  of  her  udder  thru  her 
teat  in  a  manner  special!}-  devised  to  prevent  the  occurrence  of  a 
trauma.  The  one  cow  received  live  tubercle  bacilli  of  low  virulence 
and  the  other  dead  tubercle  bacilli  of  the  same  strain.  As  a  result  of 
the  injections  the  udders  of  both  cows  were  considerably  affected  and 
secreted  a  cream}",  slightly  viscid,  fluid,  which  contained  innumerable 
leucocytes.  The  cow  that  received  the  dead  bacilli  recovered  com- 
pletely in  about  two  months,  and  the  cow  that  received  the  live  bacilli, 
while  she  made  an  apparent  recovery  in  about  eighteen  months,  con- 
tinues to  secrete  tubercle  bacilli,  virulent  for  guinea  pigs  at  this  date, 
four  years  and  ten  months  after  injection. 

The  microscopic  examinations  of  the  secretions  from  the  injected 
quarters  of  the  udders  of  the  two  cows  showed  that  the  dead  tubercle 
bacilli  were  almost  invariably  located  within  leucocytes,  and  that  the 
live  tubercle  bacilli  were  rarely  located  in  the  leucocytes  and  almost 
invariably  floated  free  in  the  fluid  in  which  the  leucocytes  were  sus- 
pended. Additional  experiments  are  now  in  progress  to  determine 
whether  this  is  always  the  case  with  tubercle  bacilli  in  the  udders  of 
cattle. 

Relative  to  the  course  followed  by  the  infectious  material  in  the  four 
tail-injected  animals  we  have  the  following  facts:  (1)  The  excessive 
disease  in  the  lung  in  all  cases;  (2)  the  presence  of  superficial  inguinal 
disease  in  all  cases;  (3)  the  infection  of  the  liver  in  the  three  hogs,  but 
not  in  the  calf;  (4)  the  infection  of  the  spleen  in  two  hogs;  (5)  the 
infection  of  the  bronchial  glands  in  one  hog  and  in  the  calf,  and,  (6)  in 
addition  to  the  infection  of  the  lung,  superficial  inguinal  and  bronchial 
glands,  the  infection  in  the  calf  of  the  coccygeal,  mesenteric,  and 
mediastinal  glands;  and,  in  addition  to  the  infection  of  the  lung,  super- 
ficial inguinal  glands,  liver,  spleen,  and  bronchial  glands  in  one  hog, 
an  infection  also  of  the  gastro-hepatic  glands. 

From  this  we  may  conclude  that  the  infectious  material,  after  it  h.al 
been  taken  up  by  the  lymph  radicals  in  the  tail,  past  more  or  In- 
directly to  the  superficial  inguinal  glands,  which  filtered  out  and 
retained  some  of  the  bacilli.  The  two  glands  at  the  root  of  the  tail  in 
the  calf  evidently  have  a  position  in  the  lymphatic  chain  between  the 
tail  and  the  superficial  inguinal  glands.  Whether  the  disease  in  the 
mesenteric  glands  of  the  calf  was  due  to  direct  transmission  of  infec- 
tion to  them  from  the  seat  of  inoculation,  or  was  due  to  bacilli  coughed 
up  from  the  lung  and  swallowed  and  past  thru  the  intestinal  wall, 
could  not  be  definitely  determined.  The  infection  of  the  liver  and 
spleen  is  probably  secondary  and  followed  after  the  infection  of  the 
lung.  The  less  amount  of  disease  in  the  livers  of  the  hogs  and  its 
entire  absence  in  the  calf  bears  out  this  assumption.  The  same  is 


12  TUBERCULOUS    LESIONS    AND    MODE    OF    INFECTION. 

true  of  the  disease  in  the  spleen,  which  was  slightly  affected  in  two 
hogs  and  normal  in  one  hog  and  in  the  calf. 

As  with  our  previously  published  experiments  in  which  hogs 
received  injections  of  virulent  tubercle  bacilli  subcutaneously  in  the 
abdominal  region,"  and  the  experiment  in  which  hogs  contracted 
tuberculosis  thru  eating  artificially  infected  milk,6  it  is  shown  with 
these  injections  that  tubercle  bacilli  may  pass  from  portions  of  the 
body  remote  to  the  lung  fairly  directly  to  it  and  cause  pulmonary 
tuberculosis.  And  this  passage  ma}7  occur  without  the  formation  or 
development  of  a  well-marked  chain  of  lesions  along  the  path  followed 
by  the  bacilli  from  the  point  of  entrance  in  the  body  to  their  localiza- 
tion in  the  lung. 

SOME   CORROBORATIVE   EVIDENCE   OF   OTHER   INVESTIGATORS. 

That  tubercle  bacilli  can  pass  thru  lymph  glands,  along  lymph  chan- 
nels into  the  great  thoracic  duct,  and  thru  it  into  the  venous  circulation, 
from  which  the  infection  of  the  lung  occurs,  is  receiving,  in  addition 
to  the  evidence  drawn  from  our  own  experiments,  the  strongest  sup- 
port from  the  work  of  other  investigators. 

According  to  a  resume  of  their  work  in  a  recent  number  of  the 
Medical  Record,0  Schlossman  and  St.  Engle  have  exprest  practically 
the  same  conclusion.  The}7  drew  it  from  the  occurrence  of  tubercle 
bacilli  in  the  lungs  of  guinea  pigs  into  the  stomachs  of  which  an 
emulsion  of  tubercle  bacilli  was  introduced  by  means  of  a  laparotomy 
especially  made  to  exclude  the  direct  infection  of  the  air  passages  or 
lung. 

Calmette  is  quoted  in  the  British  Medical  Journal ll  to  have  observed 
that  pigment  ingested  by  adult  animals  found  its  way  at  once  to  the 
lungs,  while  that  ingested  by  young  animals  was  first  stopt  by  the  mes- 
enteric  glands,  and  that  he  had  produced  a  case  of  pulmonary  tuber- 
culosis without  lesions  of  the  gastro-intestinal  mucosa  or  the  mesenteric 
glands  by  introducing  suspensions  of  tubercle  bacilli  into  tho  rumens 
of  goats. 

THE  INHALATION  AND  INGESTION  METHODS  OF  INFECTION 

CONTRASTED. 

The  practical  conclusion  to  be  drawn  from  tho  results  obtained  is 
that  ingestion  is  a  greater  danger  than  the  respiration  of  tubercle 
bacilli,  especially  as  the  tubercle  bacilli  may  be  ingested  in  the  fresh 
state  in  which  they  are  expelled  from  tuberculous  lesions  and  can  not 
be  respired  until  they  have  been  subjected  to  various  attenuating 

a Bureau  of  Animal  Industry,  Bulletin  No.  86. 
&  Bureau  of  Animal  Industry,  Bulletin  No.  88. 
cVol.  70,  No.  5,  p.  191. 
•'X...  L':!Ti»,  March  17,  11)06,  p.  623. 


INHALATION    AND    INGESTION    CONTRASTED.  13 

processes.  The  substance  in  which  tubercle  bacilli  are  enveloped  or 
embedded  when  they  leave  the  infected  organs  under  ordinary  and 
usual  conditions  requires  considerable  time  before  it  can  be  sufficiently 
dried  and  pulverized  to  float  in  the  air.  Bacilli  do  not  rise  from  moist 
surfaces  and  float  in  the  air.  The  complete  desiccation  that  must 
occur  in  advance  of  pulverization  is  either  a  comparatively  slow  process 
or  is  hastened  by  agencies,  like  the  heat  from  the  direct  rays  of  the  sun, 
that  have  a  potent  influence  against  the  vitality  of  pathogenic  bacteria. 
Sputum,  for  example,,  dries  on  the  surface  in  a  way  that  coats  it  with 
a  protective  membrane  thru  which  evaporation  progresses  slowly; 
it  is  a  very  adhesive  substance  and  becomes  more  so  during  the  first 
stages  of  drying,  and  it  must  be  exposed  when  thoroly  dried  to  actual 
attrition  before  it  can  be  detached  from  the  surface  on  which  it  has 
dried  and  reach  a  sufficient  disintegration  to  be  blown  about  as  dust. 

THE   THEORY   OF   INFECTION    BY   INHALING   DRIED   SPUTUM. 

Dried,  pulverized  sputum  has  long  been  regarded  as  the  most  pro- 
lific and  important  agent  for  the  dissemination  of  tuberculous  infec- 
tion. Koch,  in  his  Nobel  lecture  delivered  at  Stockholm  on  December 
12,  1905, a  declared  that  only  those  tuberculous  patients  who  suffer 
from  laryngeal  and  pulmonary  tuberculosis  and  whose  sputa  contain 
bacilli  are  dangerous  to  those  around  them  in  a  noteworthy  degree. 

On  the  other  hand  we  learn  from  the  investigations  of  Cadeac?'  that 
the  hypothesis  of  the  transmission  of  tuberculosis  by  inhalation  of  the 
dust  from  dried  sputa  has  not  been  proved.  He  found  that  expecto- 
rated matter  dried  slowly  and  was  neither  simple  nor  easy  to  convert 
into  dust;  that  sputa  spread  thickly  on  a  glass  plate  and  exposed  to 
natural  light  adhered  as  a  bright  varnish  and  was  not  easily  powdered 
into  dust  until  the  tenth  or  twelfth  day,  and  that  even  on  the  sixth 
day  a  considerable  quantity  of  powdered  sputum  was  required  to  cause 
a  discrete  tuberculosis  on  peritoneal  injection  of  guinea  pigs.  Sputum 
spread  on  a  marble  plate  and  kept  above  a  stove  for  fourteen  days  was 
found  to  have  lost  its  virulence  for  guinea  pigs,  and  spread  on  a  porous 
plate  and  exposed  to  sunlight  it  was  not.  effective  for  inoculation  after 
forty-eight  hours.  Dried  in  the  dark,  some  virulence  was  retained. 

THE  MORE  SERIOUS  DANGER  FROM  FRESH  AND  MOIST  TUBERCULOUS 

MATERIAL. 

We  gather  from  these  various  facts  that  too  much  importance  has 
been  given  to  dried  and  pulverized,  and  not  enough  to  fresh  and  moist 
tuberculous  material.  The  respirator}'  theory  to  account  for  the  rela- 
tively great  frequency  with  which  tuberculosis  is  localized  in  the  lung 

«  The  Lancet,  May  26,  1906. 

&Lyon  Medical,  December  10,  1905;  British  Medical  Journal,  March  10,  1906. 


14  TUBERCULOUS    LESIONS    AND    MODE    OF    INFECTION. 

really  requires  dried  and  pulverized  sputum  to  give  it  a  reasonable 
footing',  and  if  pulverized  sputum  is  shown  to  be  inert  the  theory  has 
nothing  left  to  stand  on.  With  the  respiratory  and  inhalation  theory 
shown  to  be  unnecessar}'  to  account  for  the  infection  of  the  lung,  and 
the  outline  we  have  given  of  the  manner  in  which  the  lung  becomes 
infected,  fresh  and  moist  tuberculous  material  must  be  given  a  place  of 
primary  importance,  and  exposure  to  it  must  be  persistently  avoided 
and  regarded  as  the  exceptionally  great  danger.  This  can  not  be  too 
much  emphasized. 

Exposure  to  fresh  and  moist  material  that  contains  tubercle  bacilli 
occurs  probably  with  great  frequency,  thru  the  ingestion  of  food  that 
has  been  handled  and  prepared  by  persons  affected  with  tuberculosis. 
To  quote  again  from  Koch's  Nobel  lecture,  previously  referred  to,  we 
have  the  following: 

Attention  must  be  paid  to  the  fact  that  it  is  not  only  the  secretion  of  the  lungs 
called  sputum  that  is  dangerous  as  containing  bacilli,  but  that  according  to  the  inves- 
tigations of  Flugge  the  smallest  droplets  of  phlegm  that  are  thrown  into  the  air  by 
tuberculous  persons  when  they  cough,  clear  their  throats,  and  even  when  they  speak, 
also  contain  bacilli  and  can  cause  infection. 

What  more  fruitful  source  of  food  infection  with  tubercle  bacilli  can 
exist  than  that  implied  in  the  foregoing  quotation,  when  the  culinaiy 
operations  of  a  household  are  intrusted  to  a  tuberculous  person, 
whether  servant  or  member  of  the  family,  or  when  the  food  in  an 
eating-house  or  hotel  is  prepared  by  a  tuberculous  cook  or  a  cook  with 
a  tuberculous  assistant,  or  when  food  is  exposed  to  no  further  means 
of  contamination  than  a  tuberculous  waiter,  who  breathes  over  cold  and 
hot  dishes  alike,  commonly  with  perfect  ignorance  and  disregard  of  the 
insidious  but  fatal  poison  that  may  escape  from  his  mouth  with  every 
word  he  speaks  and  everjT  accelerated  expiration  that  passes  his  lips? 

THE  FACILITY  WITH  WHICH  BACILLI  FROM  TUBERCULOUS  COWS 
MAY  ENTER  HUMAN  FOOD. 

Altho  authorities  are  not  in  accord  on  the  intertransmissibility  of 
human  and  bovine  tuberculosis,  we  feel  that  it  is  necessary  to  call 
attention  to  one  way  in  which  tubercle  bacilli,  scattered  by  tuberculous 
cattle,  are  undoubtedly  often  introduced  into  human  food. 

Tuberculosis  of  men  and  cattle  was  universally  regarded  as  etiolog- 
ically  the  same  affection  until  Dr.  Theobald  Smith,  of  America,  pointed 
out  a  morphological  difference  between  tubOrde  bacilli  isolated  from 
human  and  bovine  lesions,  and  Dr.  Robert  Koch,  of  Germany,  later 
on,  characterized  bovine  tuberculosis  as  a  disease  that  coirid  be  almost, 
if  not  entirely,  ignored  :is  a  source  of  infection  dangerous  to  man. 

()])])«»i-d  to  the  view  of  Doctor  Smith  is  the  frequent  isolation  of 
bacilli  from  human  tuberculous  lesion ^  that  arc  morphologically  of  the 
bovine  type.  This  circumstance  may  l>e  interpreted  to  mean  one  of 


HUMAN    AND    BOVINE    TUBERCULOSIS.  15 

two  things— either  that  persons  who  succumb  to  tuberculosis  due  to 
bacilli  of  the  so-called  bovine  type  were  infected  from  cattle,  or  that 
the  difference  between  the  so-called  human  and  bovine  types  has  a  sig- 
nificance similar  to  that  of  the  morphological  variation  common  with 
most  bacteria. 

Doctor  Koch's  assertion  that  cattle  tuberculosis  is  a  negligible  quan- 
tity in  the  measures  that  must  be  taken  for  the  preservation  of  human 
health  is  based  largely,  if  not  wholly,  on  negative  evidence,  or,  strictly 
speaking,  no  evidence  at  all.  He,  as  well  as  many  other  investigators, 
found  that  it  was  difficult  to  induce  tuberculosis  in  cattle  by  exposing 
them  to  or  injecting  them  with  tubercle  bacilli  obtained  from  human 
sources,  and  concluded  from  this  that  man  was  equally  resistant  to 
tubercle  bacilli  obtained  from  bovine  sources.  The  premise  does  not 
justify  the  conclusion,  and  the  mass  of  circumstantial  evidence  that  is 
contrary  to  its  acceptance  is  extremely  voluminous  and  convincing. 

Many  tubercle  bacilli  have  been  isolated  from  human  lesions  that 
are  more  infectious  for  cattle  than  many,  tubercle  bacilli  isolated  from 
lw vine  lesions,  and  it  is  now  pretty  generally  admitted  that  tubercle 
bacilli  from  bovine  sources  as  a  rule  have  a  higher  virulence  than 
tubercle  bacilli  from  human  sources  for  all  animals  with  which  they 
have  been  tested.  The  animals  tested  include  several  species  of  the 
quadrumania,  which  are  certainly  much  nearer  to  man,  anatomically 
and  physiologically,  than  to  cattle. 

It  would  be  curious  indeed  if  man  were  an  exception  to  a  rule  that 
has  been  found  by  conclusive  tests  to  be  applicable  to  the  animal 
nature  of  all  the  species  of  the  mammalian  kingdom  to  which  man 
belongs.  To  establish  definitely  that  one  species  is  an  exception  to  a 
condition  that  is  true  of  all  the  tried  species  of  a  great  kingdom 
should  require  preponderating  evidence,  and  can  not  be  settled  with 
negative  evidence  or  a  simple  process  of  reasoning  from  analogy.  In 
fact,  it  is  not  a  process  of  reasoning  at  all  with  which  we  are  dealing; 
it  is  a  simple  assumption  to  say  that  a  being  which  is  ordinarily  affected 
with  a  weaker  virus  of  a  special  kind  is  immune  against  the  stronger 
virus  usually  found  in  connection  with  another  being,  simply  because 
the  being  with  the  stronger  is  to  some  extent  immune  against  the 
weaker  virus. 

The  commonly  lower  virulence  of  tubercle  bacilli  from  human  lesions 
may  be  due  in  part  to  the  comparative!}1  greater  care  bestowed  on  sick 
persons,  and  the  general  treatment,  medical  and  other  kind,  that  they 
receive,  which  prolongs  their  lives  and  the  duration  of  the  affection, 
and  consequently  exposes  the  virus  to  possible  modifying  influences 
of  a  biologic  order.  This  seems  more  probable,  since  it  has  been  shown 
that  the  disease  has  the  elements  of  a  self -limited  affection,  by  the 
fact  that  it  is  possible  to  induce  an  immunity  against  tuberculosis  by 
the  injection  of  tubercle  bacilli  of  a  virulence  too  low  to  cause  a 
progressive  tuberculosis. 


16  TUBERCULOUS    LESIONS    AND    MODE    OF    INFECTION. 

But  we  do  not  wish  to  enter  into  a  long  argument  on  this  question, 
and  must  return  to  the  subject  of  tubercle  bacilli  from  cattle  that  may 
enter  human  food.  We  believe  that  we  have  said  enough  to  show  that 
it  is  desirable  in  every  sense  of  the  word  to  protect  our  health  against 
tuberculous  infection  from  cattle  and  to  know  thru  what  channel  it 
may  reach  us.  We  are  compelled  to  maintain  this  view,  tho  it  is 
opposed  to  the  opinion  of  Doctor  Koch,  of  the  inestimable  value 
of  whose  general  work  on  tuberculosis  we  have  the  highest  appreci- 
ation and  sincerely  feel  and  believe  that  it  gives  him  the  rank  of  a 
public  benefactor  of  the  first  order. 

It  has  been  shown  by  our  work  at  the  Experiment  Station  during 
the  past  year,  an  account  of  which  will  be  published  in  a  separate 
article,  that  the  main  channel  thru  which  tubercle  bacilli  leave  the 
bodies  of  tuberculous  cattle  is  the  rectum,  and  that  feces  may  be 
regarded  as  a  parallel  substance  with  cattle  to  sputa  with  man  in  the 
dissemination  of  tubercle  bacilli.  This  was  demonstrated  thru  micro- 
scopic examinations  and  inoculation  tests  with  small  animals. 

The  feces  not  only  of  cattle'afi'ected  with  advanced  tuberculosis,  but 
also  of  a  large  percentage  of  those  so  slightly  affected  that  their  tuber- 
culous condition  was  not  suspected  until  they  had  been  tested  with 
tuberculin,  were  found  to  contain  a  sufficient  number  of  microscopically 
discoverable  tubercle  bacilli  to  equal  many  millions  in  the  total  mass 
of  feces  past  by  a  single  cow  each  day.  The  bacilli  were  found  to  be 
evenly  distributed  in  the  feces,  which  is  fairly  good  evidence  that  they 
had  past  thru  the  greater  portion,  probably  the  entire  length,  of  the 
digestive  tract.  This  even  distribution  was  similar  to  that  of  the  bacilli 
in  the  feces  of  healthy  cattle  that  were  given  water  to  drink  to  which 
'tubercle  bacilli  had  been  intentionally  added.  That  the  bacilli  were 
virulent  was  proved  by  causing  tuberculosis  to  develop  in  guinea  pigs 
l>y  inoculating  them  with  feces  and  with  milk  soiled  with  feces  from 
naturally  tuberculous  cows,  as  well  as  from  the  healthy  cows  that 
drank  water  to  which  tubercle  cultures  had  been  added. 

Now.  if  many  millions  of  tubercle  bacilli  are  commonly  past  by 
tuberculous  cows,  evenly  distributed  in  their  feces,  which  we  have 
definitely  convinced  ourselves  to  be  the  case,  it  is  not  difficult  to  see 
that,  because  of  the  intensely  infected  environment  of  tuberculous 
cattle,  it  is  no  easy  matter  to  obtain  milk  at  all  times  free  from  tubercle 
bacilli.  How  easily  feces,  and  with  them  tubercle  bacilli,  may  be 
introduced  into  the  milk  pail  no  one  who  has  witnessed  the  milking  of 
cows  need  be  told. 

CONCLUSIONS. 

(1)  We  believe  that  we  have  shown  that  systematic  investigation  is 
gradually  retiring  the  inhalation  theory  that  has  long  been  used  to 
explain  the  frequency  with  which  tuberculosis  is  a  pulmonary  disease 


CONCLUSIONS.  17 

and  that  the  ingestion  of  tubercle  bacilli  is  being  proved  to  be  the  real 
method  thru  which  tuberculous  infection  reaches  the  lung,  as  well  as 
other  organs  of  the  body. 

When  substances  of  dissimilar  specific  gravity  move  at  the  same 
rate  of  speed  under  similar  conditions',  it  is  a  physical  fact  that  the 
force  required  to  change  their  direction  is  proportionately  greater  as 
the  specific  gravity  increases.  If  the  substances  of  dissimilar  specific 
gravity  are  air  and  dust  and  the  change  of  direction  is  due  to  move- 
ment thru  the  far-from-straight,  moist-walled  passages  from  the  nasal 
openings,  or  even  the  mouth,  to  the  lung,  the  dust  will  be  thrown 
at  every  turn,  because  of  its  greater  specific  gravity,  against  the  walls 
of  the  air  passages,  to  which  it  will  adhere  because  they  are  moist, 
and  the  ciliated  epithelium  with  which  the  respiratory  passages  are 
lined  will  tend  to  move  the  adherent  particles  outward  and  not  inward. 
It  is,  hence  (excepting,  possibly,  with  extremely  forcible  inspiratory 
movement  in  a  dust-saturated  atmosphere),  almost  a  physical  impossi- 
bility for  dust  particles  to  penetrate  with  the  air  into  the  lung.  If  no 
other  argument  than  this  could  be  brought  to  bear  against  the  inhala- 
tion theory  of  pulmonary  tuberculosis — and  it  applies  with  equal  force 
against  inhalation  of  other  infectious  material,  including  the  micro- 
organisms of  pneumonia — it  would  be  sufficient  to  condemn  it. 

(2)  Not  only  is  the  inhalation  theory  dying  and  making  room  for 
the  fact  that  ingestion  is  the  true  mode  of  infection  with  tuberculosis, 
but  the  theory  that  dust  from  pulverized  sputa  is  the  most  important 
factor  in  the  transmission  of  tuberculosis  from  subject  to  subject  is 
gradually  losing  ground  also  and  giving  wa^v  to  the  conviction  that 
fresh  tuberculous  material  must  be  lookt  to  as  the  true  agent  thru 
which  infection  occurs. 

(3)  While  many  cases  of  tuberculosis  undoubtedly  have  their  origin 
thru  food  directly  or  indirect!}"  infected  with  fresh  tuberculous  mate- 
rial by  tuberculous  persons,  there  is  no  means  to-da}7  by  which  per- 
sons are  brought  into  closer  contact  with  fresh  tuberculous  material 
than  milk  and  daily  products  obtained  from,  and  in  the  environment 
of,  tuberculous  cows.     The  wide  use  of  milk,  its  rapid  distribution 
because  of  its  perishable  character,  the  ease  with  which  it  may  be  con- 
taminated by  having  tubercle-bacilli-laden  feces  splashed,   spraj^ed, 
switched,  or  otherwise  introduced  into  it  in  a  fresh  state,  all  speak  for 
one  conclusion,  namely,  that  we  have  no  more  active  agent  than  the 
tuberculous  cow  for  the  increase  of  tuberculosis  among  animals  and  its 
persistence  among  men. 

SUMMARY   OF   THE   CONCLUSIONS. 

The  main  facts  are  as  follows: 

(a)  Tuberculosis  is  a  disease  contracted  thru  the  ingestion  of  tubercle 
bacilli. 


18  TUBEKCULOUS    LESIONS    AND    MODE    OF    INFECTION. 

(b)  The  lung  is  the  most  frequent  organ  affected,  independently  of 
the  point  at  which  the  infectious  material  enters  the  body. 

(c)  Tuberculous  infection  may  pass  from  one  part  of  the  body  to 
another  remote  to  it  without  leaving  a  chain  of  lesions  to  mark  its 
path. 

(d)  Fresh  tuberculous   material    has  the   highest,  and  dried   and 
pulverized  material  a  doubtful  significance. 

(e)  Tuberculous  material  from  cattle  has  the  highest  virulence  for 
all  tested  species  of  the  mammalian  kingdom,  to  which  man  anatom- 
ically and  physiologically  belongs,  and  tuberculous  material  from  man 
has  a  lower  virulence. 

(f)  Man  is  constantly  exposed  to  fresh  tuberculous  material  in  a 
helpless  way  thru  his  use  of  dairy  products  from  tuberculous  cows  and 
cows  associated  with  tuberculous  cattle. 

It  seems  from  this  array  of  facts,  every  one  of  which  is  based  on 
positive  experimental  evidence,  that  we  should  feel  no  doubt  regarding 
our  plain  duty,  which  is,  no  matter  what  other  measures  we  adopt  in 
our  iight  against  tuberculosis,  not  to  neglect  one  of  the  chief,  if  not 
the  most  important,  source  of  infection — the  tuberculous  dairy  cow. 


ADDENDUM. 
RECENT   WORK    BY   A   FRENCH   INVESTIGATOR. 

Since  concluding  this  article  a  recent  paper  by  Cadeac  has  appeared 
in  Le  Bulletin  Medical  of  September  5,  1906,  of  which  the  following 
resume*  was  given  in  the  New  York  Medical  Record  of  October  6, 1906, 
and  it  seems  desirable  to  quote  it  here,  because  of  its  important  bearing 
on  the  relative  danger  to  health  represented  on  the  one  hand  by  exposure 
to  dried  and  pulverized,  and  on  the  other  by  exposure  to  moist  and  fresh 
tuberculous  material : 

Cadeac  declares  that  the  dust  ground  from  dried  tuberculous  sputum  is  harmless 
both  to  the  digestive  and  respiratory  passages.  Not  a  single  experiment  has  shown 
the  transmission  of  tuberculosis  by  the  inhalation  of  dust  gathered  from  localities 
inhabited  by  tuberculous  patients.  The  writer  has  demonstrated  that  it  is  almost 
impossible  to  cause  the  development  of  this  disease  by  the  inhalation  of  this  infected 
dust.  The  desiccation  and  rapid  conversion  of  sputum  into  flying  dust  are  the 
natural  means  of  preservation  against  tuberculous  infection. 

Mere  we  have  a  double  argument,  equally  potent  against  the  inhala- 
tion theory  of  pulmonary  tuberculosis  and  in  favor  of  the  greater 
danger  from  exposure  to  fresh  and  moist  tuberculous  material.  A- 
\\<-  have  already  said,  without  dried  and  pulverized  infectious  material 
the  inhalation  theory  has  absolutely  no  foundation  on  which  it  can 
reasonably  stand;  and,  if  dried  and  pulverized  material  is  as  inert  as 
the  investigations  of  Cadeac  represent  it  to  be,  fresh  and  moist  material 
for  men  and  animals  alike  must  be  lookt  to  as  the  true  cause  for  the 


ADPENDUM.  19 

transmission  and  persistence  of  tuberculosis.  The  inhalation  theory,  and 
the  great  importance  attached  to  dust  as  an  agent  for  the  transmission 
of  tuberculosis,  are  beginning  to  have  the  appearance  of  two  errors 
that  have  long  hampered  the  fight  that  is  being  made  against  tuber- 
culosis. A  clear  comprehension  of  the  many  ways  in  which  fresh 
tuberculous  material,  the  infectious  potency  of  which  is  unquestionable, 
can  be  introduced  into  articles  of  food  used  by  man  and  animals,  shows 
conclusively  that  this  is  sufficient  to  account  for  the  frequency  with 
which  infection  occurs  and  the  widespread  character  of  the  disease. 


O 


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